This invention relates in general to vehicle hydraulic brake systems, and in particular to dual circuit master cylinders incorporated in such vehicle hydraulic brake systems.
Conventional vehicle hydraulic brake systems commonly have two hydraulic circuits: a primary circuit and a secondary circuit. For a vehicle having four wheel brakes in which there is a pair of front wheel brakes and a pair of rear wheel brakes, the primary and secondary circuits can be connected to the wheel brakes by various configurations, such as a diagonally split arrangement or a vertically split arrangement. In a diagonally split arrangement, the primary circuit is connected to one of the front wheel brakes and also to one of the rear wheel brakes on the opposite side from the connected front wheel brake. The secondary circuit is then connected to the other front wheel brakes and the other rear wheel brake on the opposite side of the connected front wheel brake. In a vertically split arrangement, the primary circuit is connected to, for example, the front wheel brakes, and the secondary circuit is connected to the rear wheel brakes. The use of two brake circuits helps to maintain a source for braking of the vehicle in case of failure of one of the brake circuits.
A dual circuit or tandem master cylinder is often used to supply pressurized fluid to each of the primary and secondary brake circuits. A tandem master cylinder generally includes a pair of pistons which are operatively connected to a brake pedal which is operated by the driver of the vehicle. Actuation of the brake pedal causes movement of the pistons which energize separate fluid chambers in fluid communication with the primary and secondary brake circuits, respectively.
Such tandem master cylinders, however, can have significant drawbacks if one of the brake circuits should fail. For example, upon failure of one of the brake circuits, the piston stroke of the master cylinder can rapidly increase, thereby causing the brake pedal to "drop" or travel an undesirable relatively large distance. This pedal drop can cause great alarm to the operator of the vehicle and possibly produce a panic situation for the operator. Thus, a relatively large pedal drop during a single circuit failure is an undesirable quality.
For this reason, it would be desirable to have a tandem master cylinder in which pedal drop reduced in the event that one of the brake circuits should fail.